Being Exo's Little Sister

Kim Raeseok is the little sister of Xiumin from Exo-M. Xiumin hasn't seen his sister in over 2 years. While they were separated, she had a boyfriend named Mung and he was abusive towards her. What happens when she dumps him and Xiumin along with the rest of Exo find the marks he left on her? He told her he would get r...